Method of preventing crystals from forming in creosote and the resulting product



United States Patent 3,376,212 METHOD OF PREVENTING CRYSTALSv FROM FORMING IN CREOSOTE AND THE RESULT- ING PRODUCT Philip X. Masciantonio, Penn Township, Westmoreiand County, and Myron H. Wilt, Monroeville Borough, Pa., assignors to United States Steel Corporation, a corporation of Delaware No Drawing. Filed Feb. 10, 1966, Ser. No. 526,353 3 Claims. (Cl. 208-2) ABSTRACT OF THE DISCLOSURE Prevents undesirable formation of crystals in creosote. Creosote treated with a gaseous olefin as an alkylating agent in the presence of an aromatic sulfonic acid catalyst. The crystal-forming compounds are converted to alkyl derivatives, which are soluble in creosote,

This invention relates to an improved method of pre venting crystals from forming in creosote and to the resulting creosote product.

Creosote is a coal-tar distillation product which may be considered as composed of three fractions, (1) light creosote which boils at about 270 to 315 C., (2) middle creosote which boils at about 315 to 355 C., and (3) heavy creosote which boils above about 355 C. The substances which crystallize are anthracene threne, and they occur mainly in middle cresote. As a wood preservative, creosote can provide maximum protection only if it completely saturates the wood. Crystals plug the pores of the Wood and prevent proper penetration of the cresote into the pores. Another problem is that crystals settle when creosote is transported or stored. They segregate at the botom of a tank car or barge, where they are troublesome to remove.

Several techniques are known for freeing finished creosote of crystals, but each has disadvantages. One possibility is to cool the creosote in large tanks in which crystals settle, and decant off crystal-free creosote. This is time-consuming and requires a considerable investment in storage vessels. Another possibility is to cool the creosote and remove crystals in a centrifuge or filter, but this also is costly. A third possibility is to eliminate middle creosote by distillation, and use a blend which consists only of light and heavy creosotes.

All these procedures result in an economic loss, since recovered crystals or middle creosote are useful only as fuel. Still another possibility is to add an appropriate coaltar fraction to the creosote as a solvent or diluent, but there are limits to the quantity of low-boiling constituents which can be present in creosote. Generally the material added is more valuable than creosote.

An object of our invention is to provide an improved method of preparing creosote so that it is substantially free of crystals, but overcoming disadvantages of techniques known heretofore.

A further object is to provide a method of accomplishing the foregoing object in which the crystals are rendered soluble in the remainder of the creosote by treatment with an alkylating agent in the presence of an acid catalyst A further object is to provide an improved creosote product in which the crystal-forming substances are in solution by virtue of the foregoing treatment.

According to our invention, we treat creosote with a gaseous olefin in the presence of an aromatic sulfonic acid. The olefin serves as an alkylating agent which converts anthracene and phenanthrene to the corresponding alkyl derivatives. We prefer propylene, but we can use Olefins of higher molecular weight, provided they do not and phenan- 3,3 76,2 12 Patented Apr. 2, 1968 lead to side reactions in which undesirable compounds form. Olefins or molecular weight lower than propylene do not appear suitable. The aromatic sulfonic acid serves as a catalyst. We prefer toluene sulfonic acid, but we can use sulfonic acids of other aromatics, such as benzene, naphthalene or phenanthrene. We add about 2 to 20 percent by weight of the acid based on the weight of creosote, heat the mixture to a temperature of about to C., and bubble gaseous olefin through this mixture for about 1 to 6 hours. We prefer a temperature close to 150 0, since the reaction is undesirably slow at lower temperatures. The catalyst decomposes at temperatures above 150 C., as evidenced by an odor of sulfur dioxide. We may treat only the middle creosote and blend the treated product with light and heavy creosotes, or alternatively treat the whole creosote and avoid the need to isolate middle creosote.

The presence of impurities in the creosote, such as nitrogen bases, sulfur-containing heterocyclic compounds, and oxygenated compounds, hinders the alkylation reaction, since these compounds react with the catalyst. However, the alkylation reaction proceeds even though such impurities are present, as long as sufficient catalyst is added. To conserve catalyst we prefer to remove the impurities prior to alkylation by washing the creosote with sodium hydroxide and sulfuric acid. The removal of impurities from specific creosote fractions may not be necessary, since the concentration of impurities depends largely on the boiling range of the fraction and the type of coal tar.

We can alkylate the creosote in an ordinary steel vessel and we use relatively inexpensive materials Our treatment increases the volume of creosote available for marketing, since we' utilize the crystal-forming substances where otherwise they are discarded. Besides eliminating crystals, our treatment provides improved viscosity and boiling characteristics. It is desirable to include high-boiling components in creosote to minimize evaporation. Alkylated middle creosote has a boiling point about 50 C. higher than the original middle creosote. Bleeding is a problem in creosote-treated wood. It is desirable to include high-viscosity components in creosote to minimize this problem, since they are less prone to bleed.

Specific examples to illustrate how we may practice the invention are as follows:

EXAMPLE 1 We introduced to a reaction vessel 100 parts by weight of middle creosote and 20 parts by weight p-toluene sulfonic acid. We heated this mixture to 150 C. We stirred the mixture and bubbled propylene gas through it for a three-hour period while maintaining it at this temperature. By this treatment we obtained about 150 parts of liquid product. We cooled this product and blended it with 600 parts of a mixture of light and heavy creosotes, and thereby produced a crystal-free specification creosote.

EXAMPLE 2 We alkylated middle creosote by the procedure described in the foregoing example. We blended the alkylated product with an equal quantity of untreated middle creosote. We blended the resulting product with appropriate quantities of light and heavy creosotes and again produced a crystal-free specification creosote.

From the foregoing description and examples, it is seen that our invention forms a simple effective method of preparing creosote which is free of crystals. The product not only is improved by elimination of crystals, but also has a higher viscosity and boiling range, as already explained. At the same time we overcome disadvantages of previous techniques for eliminating crystals.

While we have shown and described certain preferred embodiments of our invention, it is apparent other modifications may arise, Therefore, we do not wish to be limited to the disclosure set forth but only by the scope of the appended claims.

We claim:

1. A substantially crystalfree creosote product in which creosote obtained by coal tar distillation is treated with a gaseous olefin as an alkylating agent at a temperature of about 100150 C. for about 1 to 6 hours in the presence of aromatic sulfonic acid catalyst, said catalyst being selected from the group consisting of toluene sulfonic acid, benzene sulfonic acid, naphthalene sulfonic acid, and phenanthrene sulfonic acid and being used in proportions of 2 to 20 percent by weight of catalyst based on the weight of creosote treated.

2. A product as defined in claim 1 in which the olefin is propylene.

3. A product as defined in claim 1 in which the creo- 4 sote is washed with sodium hydroxide and sulfuric acid prior to treating to eliminate impurities which react with the catalyst.

References Cited UNITED STATES PATENTS 1,812,829 6/1931 Miller 208-2 2,014,766 9/1935 Isham 260-671 2,838,447 6/ 1958 Savercool 208-2 2,916,432 12/1959 McNamara 208-2 10 2,988,477 6/1961 Beaumont et ai 167-31 3,278,377 10/1966 Ferrucci 167-29 OTHER REFERENCES Chemical Abstract, vol. 53, No. 10, May 25, 1959, 15 C01. 8605a.

DANIEL E. WYMAN, Primary Examiner. P. KONOPKA, Assistant Examiner. 

